<%@ page language="java" pageEncoding="UTF-8"%>
<%@ page contentType="image/jpeg"
    import="java.awt.*,java.awt.image.*,java.util.*,javax.imageio.*"
%>
<%!
  Color getRandColor(int fc,int bc){ //给定范围获取随机颜色
      Random random = new Random();
      if(fc>255)
      fc = 255;
      if(bc>255)
      bc = 255;
      int r=fc+random.nextInt(bc-fc);
      int g=fc+random.nextInt(bc-fc);
      int b=fc+random.nextInt(bc-fc);
      return new Color(r,g,b);
  }
 %>
<% 
//设置页面不缓存
response.setHeader("Pragma","No-cache");
response.setHeader("Cache-Control","no-cache");
response.setDateHeader("Expires",0);
//在内存中创建图像
int width = 60,height = 20;
BufferedImage image = new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB);
//获取图像上下文
Graphics g = image.getGraphics();
//生成随机类
Random random = new Random();
//设定背景颜色
g.setColor(getRandColor(200,250));
g.fillRect(0,0,width,height);
//设定字体
g.setFont(new Font("Times new Roman",Font.PLAIN,18));
//画边框
//g.setColor(new Color());
//g.drawRect(0,0,width-1,height-1);
//随机产生155条干扰线，使图像中的认证码不易被其他程序探测到
g.setColor(getRandColor(160,200));
for (int i=0;i<155;i++){
  int x=random.nextInt(width);
  int y=random.nextInt(height);
  int x1=random.nextInt(12);
  int y1=random.nextInt(12);
  g.drawLine(x,y,x+x1,y+y1);
}
//取随机产生的认证码（4位数字）
String sRand = "";
for(int i=0;i<4;i++){
  String rand = String.valueOf(random.nextInt(10));
  sRand += rand;
  //将认证码显示到图像中
  g.setColor(new Color(20 + random.nextInt(110), 40+random.nextInt(110),60+random.nextInt(110)));
  //调用函数出来的颜色相同，可能是因为种子太接近，所以只能直接生成
  g.drawString(rand,13*i+6,16);
}
//将认证码显示到session
session.setAttribute("rand",sRand);
//图像生效
g.dispose();
//输出图像到页面
ImageIO.write(image,"JPEG",response.getOutputStream());
out.clear();
out = pageContext.pushBody();
%>

